The standard operative treatment for relief of left ventricular outflow obstruction secondary to idiopathic hypertrophic subaortic stenosis is a left ventriculomyotomy and myectomy and has been performed in 400 patients. Eleven patients have undergone mitral valve replacement as primary or secondary treatment of IHSS. Special considerations for mitral valve replacement in these patients include thin septum - less than 18 mm (5 pts), reoperation for persistent obstruction following a left ventriculomyotomy and myectomy (3 pts), mitral regurgitation secondary to endocarditis (2 pts) and atypical septal morphology (1 pt.) A low profile prosthesis was used in these patients, 8 Bjork-Shiley and 3 Hancock porcine bioprostheses. No operative or late mortality has occurred and 1 patient required a closure of a perivalvular leak 6 months after MVR. Six month evaluation of 4 patients has revealed good clinical and hemodynamic improvement. Mitral valve replacement should be considered in patients with obstructive IHSS under special circumstances but not as the preferred operative treatment.